Z buffer read from exr file is all ones
You just need to disable the compositor in Output Properties &gt; Post Processing &gt; Pipeline &gt; Compositing. Basically if compositing is enabled only the Image pass gets forwarded to the composite node (even if Nodes weren't enabled) and the Depth defaults to Z=1.000

If you do need to use the compositor, make sure you also link Depth to the composite node to get an exr file with a correct Z channel: